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At least another decade of satellite observations are needed before scientists can determine the rate at which ice sheets in Greenland and Antarctica are melting, according to a new report.

Until then, it isn't yet possible to determine whether the melt is due to long-term trends such as global warming or short-term natural fluctuations, and whether the current rate of melting will change in the future.

The study, which appears today in the journal Nature Geoscience examined data collected by the Gravity Recovery and Climate Experiment (GRACE) satellite from 2003 to 2012.

GRACE measures changes in the gravity field above the ice to determine the ice sheet's mass distribution, as well as movement into the ocean.

Study lead author, Dr Bert Wouter of the University of Colorado, says the satellite observed "the ice sheets are losing substantial amounts of ice -- about 300 billion tonnes each year -- and the rate at which these losses occurs is increasing."

"Compared to the first few years of the GRACE mission, the ice sheets' contribution to sea-level rise has almost doubled in recent years."

The researchers compared the satellite data with reconstructions -- based on ground measurements -- of about 50 years of mass changes to the ice sheets.

"We find that the record length of space-borne gravity observations is too short at present to meaningfully separate long-term accelerations from short-term ice sheet variability," the researchers write.

The uncertainity surrounding the rate of ice-loss means current models of sea-level rise due to melting ice sheets by 2100, could be out by as much as 35 centimetres, say the reserchers.

But it may not be too long before enough data is available to better predict the rate of ice loss. The researchers suggest that there may be enough data to detect a speed-up in mass loss of the Antarctic ice sheet, and that another 10 years of satellite observation is needed for Greenland.

Predicting the future

While there is strong evidence that sections of the Greenland and Antarctic ice sheets are melting, climate scientists are reluctant to predict what they will look like by the end of the century.

"The science community has always been aware that it may not be appropriate to extrapolate the acceleration of ice mass loss observed in the satellite-based observations to 2100 given the short length of the observations which extend back to the late 1980s," says Professor Tim Naish, Director of the Antarctic Research Centre at the Victoria University of Wellington in New Zealand.

"This is why the community and the IPCC do not base their assessment of future ice sheet contribution to sea-level rise on the satellite data alone."

Unlike the Arctic ice sheet - which floats on water - the Greenland and Antarctic ice sheets are predominately on land. They contain more than 99 per cent of the Earth's glacial ice, and according to some estimates would increase global sea levels by more than 60 metres if they completely melted.